1. Field of the Invention
The present invention relates to a hermetic compressor, more particularly, a hermetic compressor in which an oil supplying hole for supplying oil between a piston and a cylinder block is formed to pass through an inner wall of( a piston hole in which a lateral pressure of the piston is generated so as to improve a lubricating action for the piston.
2. Description of the Related Art
As shown in FIG. 1, a conventional hermetic compressor comprises a compressing instrument 20 and an electric instrument 30.
The compressing instrument 20 comprises a bearing 21 which is upright mounted at a center portion of a sealed housing 10, a crankshaft 23 which is rotatably mounted in the bearing 10 and provided with a eccentric shaft 22 at a lower portion thereof, a cylinder block 24 which is fixedly disposed at a lower portion of the bearing 21, a connecting rod 25 which is coupled to the eccentric shaft 22 of the crankshaft 23, a piston 26 which is mounted at an end of the connecting rod 25 so as to linearly reciprocate within the cylinder block 24, and a head cover 27 which is disposed at an end of the cylinder block 24 and formed with a suction and discharge valve (not shown) as means for sucking and discharging refrigerant.
And, the electric instrument 30 comprises a rotor 31 which is coupled to the crankshaft 23 so as to rotate along with the crankshaft 23, and a stator 32 which is disposed around the rotor 31 in the sealed housing 10 so as to generate an electromagnetic force by which the rotor 31 is rotated.
At a lower portion in the sealed housing 10, there is provided cooling oil 0. The cooling oil is supplied to each sliding member by a lubricating means so as to prevent a friction and wear between the sliding members.
In an example of the lubricating means, as shown in FIG. 2, there is formed a small diameter portion 41 at a middle portion of the crankshaft 23 which is inserted into the bearing 21. Between the small diameter portion 41 and an inner wall of the bearing 21, there is formed an oil bank in which the oil 0 is stored. A lower oil supplying groove 43 and an upper oil supplying groove 44 are respectively formed at each outer face of a lower and upper portions of the crankshaft 23 with the small diameter portion 41 in the center. An oil supplying hole 45, which is communicated with the lower oil supplying groove 43, is formed within the eccentric shaft 22 which is provided to the lower portion of the crankshaft 23. The oil supplying hole 45 is connected with an oil pickup tube 46. Further, at an edge of the upper end of the bearing, there is formed a guiding groove 47 for guiding the oil 0.
In the conventional hermetic compressor as described above, if power source is applied to the compressor, the rotor 31 is rotated by the electromagnetic action between the stator 32 and the rotor 31. The crankshaft 23, which is coupled to the rotor 3l, is rotated. Due to the rotation of the crankshaft 23, the eccentric shaft 22 disposed at the lower portion or the crankshaft 23 is also rotated. Therefore, the piston 26, which is coupled to the end of the connecting rod 25, is linearly reciprocated in the cylinder block 24 so that the suction, compression and discharge operations of the refrigerant are performed.
Meanwhile, when the crankshaft 23 is rotated, the oil 0 stored in the lower portion of the sealed housing 10 is sucked through the oil pickup tube 46 which is coupled to the lower portion of the eccentric shaft 22. The sucked oil 0 is moved upward through the oil supplying hole 45 and the oil supplying groove 43 and supplied to the outer face of the bearing 21. The sucked oil 0 is also supplied between the piston 26 and cylinder block 24 so that the piston 26 is smoothly reciprocated.
As described above, when the crankshaft 23 is rotated, the oil 0 is supplied to each sliding members of the compressor and then returned to the lower portion of the sealed housing 10, repeatedly.
In the conventional hermetic compressor, however, when the refrigerant is compressed, the compression force of the piston 26 is characterized by a longitudinal component force Fv and a lateral component force Fs. At this time, a clearance between the inside wall of the cylinder block 24 and the outside wall of the piston 26 is different according to the positions where the lateral component force Fs is applied or not applied (Cs1 greater than  greater than Cs2).
Therefore, when manufacturing the piston 26 and the cylinder block 24, if a machining error is generated and a foreign matter is introduced therein, an oil film is instantaneously and repeatedly destroyed in a portion between the outer wall of the piston 26 and the inner wall of the cylinder block 24, on which the lateral component force is exerted. Therefore, the lubricating action is not performed smoothly so that the friction and wearing is generated in the portion on which the lateral component force is exerted.
In the conventional mechanism, as shown in FIG. 4, since the oil 0 sucked through the oil suppling hole 45 is supplied to oil hole 24a formed at a center portion of the cylinder block 24 corresponding to a center of the piston 26, there is a problem that the oil 0 is not supplied sufficiently to the portion on which the lateral component force is exerted.
Further, there is other problem that an internal temperature of the compressor is increased by a frictional heat so as to lower the performance and the compressing implement is deformed so as to lower the confidence thereof.
It is therefore an object of the present invention to provide a hermetic compressor which has an improved lubricating structure of the piston in order to prevent the friction and wear between the piston and the cylinder block.
To achieve the above objects and other advantages, there is provided a hermetic compressor in which an oil hole is formed in the cylinder block so as to penetrate through a piston hole of the cylinder block so that oil sucked through an oil supplying hole of a crankshaft by rotation of the crankshaft is passed through the piston hole when the oil is dispersed, characterized in that the oil hole is formed at an interior wall of the piston, on which a lateral component force is exerted when the piston is reciprocated in the piston hole of the cylinder block.
Preferably, the oil hole has a larger upper diameter which is at an upper portion of the piston hole than a lower diameter which is at a lower portion of the piston hole.